Integrated circuit oscillators typically employ an external frequency determining element and the prior art circuits are notorious for generating spurious signals and adversely reacting upon the frequency determining capability of the external element. Many prior art circuits are unsuitable because of their excessive response to termperature changes. Typically, prior art circuits employ capacitors to provide the signal feedback required for oscillation. IC capacitors fabricated into the substrate as a p-N junction require special isolation and display stray capacitance, their capacitance varies with voltage, and they require considerable IC chip area. Furthermore, their characteristics are a strong function of temperature. When the capacitors are fabricated into the IC oxide, thin oxides must be used and the actual capacitors value is difficult to control. This makes them difficult to integrate into a manufacturing process. Finally, capacitor feedback circuits often introduce phase shift to their own and thus tend to pull the oscillator frequency and introduce frequency instability problems.
Many prior art circuits have been direct coupled to avoid capacitors and this approach will remove some of the deleterious capacitance-related effects. However, when a transistor collector is connected directly to a base, the available signal swing is greatly reduced. Also, even with severely restricted signal swing, nonlinearities and even rectification effects are encountered. These result in spurious signal production and detract from fequency stability.